The present invention is directed to flow meters which are used to measure the amount of fluid being dispensed or pumped. More particularly, the present invention is directed to flow meters which are precalibrated to accurately meter the flow of a variety of different fluids. The present invention is further directed to air flow compensators which can be used to compensate fluid flow measurements for air that passes through flow meters.
There are inherent internal leakage or xe2x80x9cslippagexe2x80x9d problems which effect the accuracy of flow meters, particularly volume displacement meters. Fluid which leaks or xe2x80x9cslipsxe2x80x9d by the mechanical structures intended to monitor fluid flow does not contribute to the counting mechanism and thus must be accounted for by other means, such as adjusting gear ratios on mechanical counters or multiplying factors on electronic readouts.
The main cause of variation in the amount of slippage is the viscosity of the fluid. Thin or less viscous fluids tend to experience a greater amount of slippage than thick or more viscous fluids. Accordingly, for best accuracy, flow meters must be calibrated whenever fluid viscosities change significantly. In addition to varying between different fluids, viscosities can vary over temperature ranges.
Present flow meters are either precalibrated for a particular fluid or otherwise designed to be field calibrated. Precalibrated flow meters have the disadvantages of being limited for use with a particular fluid viscosity, and not being able to compensate for temperature related changes in viscosity. Field calibrated flow meters require pumping or dispensing of a small quantity of a fluid during calibration. This can present problems when using hazardous or expensive materials since the meter will not accurately measure the volume of fluid used to calibrate the meter. Moreover, containment or recovery of the volume of fluid used to calibrate the meter may be awkward, particularly if the fluid to be dispensed is stored in a container equipped with one-way valves which prevent the user from putting fluid back into the container.
The present invention provides for precalibrated flow meters which allow a user to accurately dispense or pump a variety of fluids without recalibrating the meter for each fluid.
According to other features, characteristics, alternatives and embodiments which will be understood as the description of the present invention proceeds, the present invention provides a precalibrated flow meter which includes:
a body having an inlet and an outlet;
a fluid driven element within the body which moves in response to fluid flow between the inlet and outlet;
a memory storage device for storing a plurality of calibration factors which correspond to different fluid viscosities;
means for selecting one of the plurality of calibration factors; and
means for calculating fluid flow between the inlet and outlet from the selected one of the plurality of calibration factors.
The present invention further provides a precalibrated flow meter which includes:
a body having a chamber with a fluid inlet and a fluid outlet;
a cover which closes a top of the chamber;
a cap which couples to the body and defines a compartment;
a fluid driven element within the chamber; and
an electronics module within the compartment which includes:
a memory storage device for storing a plurality of calibration factors which correspond to different fluid densities;
means to select one of the plurality of calibration factors; and
means for calculating fluid flow between the inlet and outlet from the selected one of the plurality of calibration factors.
The present invention also provides an air flow compensator which includes:
a fluid flow passage;
a pair of electrical probes for sensing air flow through the fluid flow passage based upon electrical properties of fluids; and
means to transfer an electrical signal which corresponds to sensed air flow through the fluid flow path.